1. Field of the Invention
The present invention generally relates to structures with functional length scales measured in nanometers, and more particularly, to methods of making the same. The nanostructured assemblies may have application in electronic, optical, and magnetic storage devices.
2. Description of the Related Art
As the limits in miniaturization of silicon based electronic devices and magnetic storage systems appear on the horizon, new generations of nano-devices are attracting attention. Contenders in the nanoscale world of electronics and storage technology include single electron transistors, nanotubes, molecular wire crossbar memory, nanoscale patterned magnetic arrays and so on. Although significant switching characteristics have been demonstrated in these systems, the assembly, interconnection and addressing of such nanostructures for logic or memory chips, magnetic storage systems remains a formidable challenge. This is a consequence of the difficulties of manipulation of nanoscale elements even in a laboratory environment.
Previous methods of making submicron-based electronic devices have included electron beam lithographic techniques, the moving of nanoparticles using scanning tunneling microscopes (STM) to create an xe2x80x9celectromechanical paintbrushxe2x80x9d to transfer electroplatable material (see U.S. Pat. No. 5,865,878), nanoimprint lithography (microcontact printing) and other approaches that use molecular self-assembly. Unfortunately, the art lacks techniques that can modulate a nanoparticle/substrate interaction to selectively self-assemble nanoparticles or molecules in an effective manner.
Accordingly, the present invention is directed to a method for assembling arrays of small particles or molecules using an atomic force microscope to modulate a nanoparticle/substrate interaction to selectively self-assemble nanoparticles or molecules, wherein the method substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for producing patterns for interconnections between devices in high density nanoscale electronic circuits or to selective patterned magnetic arrays for high density magnetic storage media. The invention provides advantages over conventional lithographic techniques used to assemble electronic devices or magnetic storage systems in the nanometer scale, or when moving the nanoparticle or molecules with atomic force microscope (AFM) tip. Direct manipulation or positioning of nanostructures with an AFM tip is difficult, requiring constant monitoring to assure the fidelity in the transport and delivery and attachment of the selected particle or molecule to desired position on the substrate. The method of the invention modulates the nanoparticle/substrate interaction to selectively self-assemble nanoparticles or molecules.
Stable ferroelectric domains on the nanometer scale can be prepared in various states of remnant polarization by means of an atomic force microscope (AFM) using a properly biased metal tip. This allows persistent patterning of the surface potential with nanoscale resolution which can then be used to draw the locus where the nanoparticles or molecules will be induced to assemble by the strong localized electrostatic interaction when deposited from a solution with non-polar solvent or where selective molecular decomposition in a chemical vapor deposition (CVD) process occurs. The invention assembles a pattern of nanoparticles or molecules for electronics applications by nanopatterning the surface potential of a ferroelectric thin film and using this surface potential to selectively adsorb the nanoparticles or molecules.
Primary features of the method are the ability to produce an arbitrary pattern of electric polarization at a free surface of a thin film, the exposure of this free surface to a solution containing chemical species that selectively adsorbs or accumulates under the influence of electrophoretic forces in a selected region of a substrate being processed. The molecules or particles may either be electrically charged species (electrophoretic) and there for attracted selectively to regions of charge opposite to their own. Alternatively, the species may be highly polarizable but uncharged and thus be attracted to areas with the high electric field gradients generated by the polarized surface regions (dielectrophoretic).
Thus, another object of the invention is to provide a method for assembling arrays of small particles using an atomic force microscope by depositing a ferroelectric thin film on a substrate; tracing a pattern on said ferroelectric thin film with said AFM thereby leaving a pattern of domains on said thin film; and exposing said ferroelectric thin film to a composition having nanosized particles, said particles coated with an organic species that selectively accumulate in said traced pattern of said thin film.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the method particularly pointed out in the written description, drawing and claims hereof.